The Effect Of The Microstructure Parameters Of Porous Silicon On Thermal Conduction And Thermal Rectifier

Porous silicon materials attract lot of attention of researchers since the end of the last century.With the development of industrial technology in recent years,porous sili--con is widely used in SOI technology,microelectronics and microsensor.The silicon nanostructure materials can be used for thermoelectric energy conversion,therefore they are promising materials for nergy and environmental protection applications.It is important to study the relationship beteen the preparation conditions of porous sili--con and its microstructure,thermal conductivity and thermal rectification.The pore size,thickness,porosity,thermal diffusivity coefficient and thermal rectification of PS samples were studied in this paper.In order to study the influence of corrosion current density on the microstructure of PS samples,the self-supporting PS samples were prepared by single-channel elec--trochemical etching.The micro-morphology of PS samples was observed by scan--ning electron microscopy(SEM).Through analyzing the morphological characters of PS by SEM,the following results were found:1?the corrosion reaction is limited to the region where the current flows;2?the pore size,thickness and porosity of PS increased as the current increased.The pore diameter were in the range of 4-13nm,that is to say,nano PS samples can be prepared by the method;3?the PS can be electro--polished When the current is 200mA/cm2.In order to study the effect of corrosion current density and temperature on the thermal properties of PS samples,the laser flash method would be used to measure the thermal diffusivity of PS samples.We can conclude through the results that the increase of temperature and corrosion current would result in the decrease of thermal diffusion coefficient of the PS samples.In order to study the thermal rectification performance of PS samples at room temperature and high temperature,the thermal diffusion coefficient of PS samples in both positive and negative directions was measured.The results show that the PS samples have a thermal rectification effect.Thermal rectification coefficient of PS sample increases as the temperature decreases,and porosity increases.When the corrosion current density is 100mA/cm2 and the measured temperature is 50 ?,the thermal rectification coefficient can reach 1.86 optimally.